1. Field of the Invention
The present invention relates to a throttle positioner which is attached to a carburetor for the purpose of reducing the emission of harmful gases, especially HC (Hydrocarbon) gases from an automobile in its decelerating condition.
2. Description of the Prior Art
When an automobile is decelerated, a throttle valve of the carburetor is generally closed to its idling position while the engine is still rotating at a relatively high speed. Thus, a relatively high vacuum is generated in an intake tube of the engine with the result that fuel which has been attached to the inner wall of the intake tube is rapidly vaporized and rich fuel air mixture is supplied to engine cylinders. Therefore, incomplete combustion of fuel is caused, resulting in a high increase in the amount of uncombusted components such as HC included in the exhaust gas. Furthermore, due to an extreme reduction of the amount in the intake fuel air mixture, the ratio of exhaust residue increases with the simultaneous increase in the possibility of misfiring. As a countermeasure to this problem, it has been proposed to hold the throttle valve at a predetermined position which is slightly opened from the idling position thereby to increase the amount of intake mixture at a level sufficient to maintain the complete combustion process in the engine. Such a means is called a throttle positioner.
A conventional throttle positioner will now be explained with reference to FIG. 1. An intake tube 1 of a carburetor is mounted with a throttle valve 2, which is adapted to rotate around a shaft 18 from its almost completely closed idling position shown in phantom lines toward an optionally opened running position by being actuated by a throttle operating mechanism (not shown) in accordance with the depression of an acceleration pedal. Relatively close to the idling position, a throttle positioner opening position is provided as shown by the solid lines wherein the throttle valve is opened just enough to reduce the intake vacuum in a decelerating condition sufficiently to accomplish complete combustion and suppress emission of uncombusted components. The throttle valve 2 is rotatably mounted on the shaft 18 and rotates therearound as a unitary body with an arm 3. The arm 3 is provided with a stopper screw 15 at one end thereof, said stopper screw being adapted to abut against a stopper 16 thereby holding the throttle valve at its idling position. The other end of the arm is adapted to abut against a stopper screw 14 provided at one end of a lever 4 which is pivoted around a shaft 19. The other end of the lever 4 is connected to a diaphragm 7 by a rod 8, said diaphragm being mounted in a diaphragm case 5 and applied with a biasing force by a compression coil spring 6 abutting against its underside. A diaphragm chamber 9 housing the spring 6 communicates with the inside of the intake tube 1 by a conduit means 11 including an air chamber 12 and a constricting means 17. The diaphragm chamber 9 is selectively supplied with vacuum through the conduit means 11, whereas a diaphragm chamber 10 is constantly supplied with atmospheric pressure. In this structure, when the diaphragm chamber 9 is not supplied with vacuum, the diaphragm is biased upward as seen in the drawing by the action of the compression coil spring 6, whereby the lever 4 is rotated counterclockwise by way of the rod 8 so that the stopper screw 14 traverses the rotary trace of the associated end of the arm 3 and holds the throttle valve 2 at the throttle positioner opening position which is slightly opened from the idling position.
However, if the throttle positioner is operated in the idling condition of the engine, the idling speed of the engine becomes high, making the driver uncomfortable as well as adversely affecting the fuel consumption rate. When the engine is decelerated while it is operating at a relatively low speed, an extremely high vacuum is not generated in the intake tube, and misfiring is generally not caused and emission of HC is usually very low. Therefore, the throttle positioner must not be operated in the idling or decelerating condition at a low speed, but rather the throttle positioner is to be operated only when the engine is decelerated while operating at a high speed above a predetermined level. In order to lock the operation of the throttle positioner when the engine is decelerated while it is operating at a low speed, the open end 13 of the vacuum conduit 11 is positioned to open to the inner wall of the intake tube 1 slightly downstream of the position where the end of the throttle valve 2 opposes the wall of the intake tube when it is positioned at the throttle positioner opening position to reduce emission of uncombusted components. Thus, when the acceleration pedal has been depressed, the opening 13 is applied with substantially atmospheric pressure whereas it is applied with a vacuum only when the throttle valve is in the range between the idling position and the position set by the throttle positioner. Therefore, as long as the engine is operating at a low speed or decelerating condition with the throttle valve 2 being positioned within a region not to traverse beyond the open end 13, the vacuum in the intake tube is always applied to the diaphragm 7, whereby it is pulled downward, turning the lever 4 clockwise as seen in the drawing by way of the rod 8 so that the stopper screw 14 is held out of engagement with the throttle arm 3. In this condition, the throttle valve 2 returns to its idling position as shown by phantom lines.
When the vehicle is running above a predetermined speed, the throttle valve 2 is opened beyond the open end 13 by stepping on the acceleration pedal, wherein the open end 13 is positioned upstream of the throttle valve 2. In this condition, the diaphragm chamber 9 is supplied with atmospheric pressure, and therefore, the lever 4 is held in the position as shown in FIG. 1 by the action of the spring 6. Then, if the acceleration pedal is released to effect deceleration, the throttle valve 2 is returned to the position as shown by solid lines determined by engagement of the stopper screw 14 of the lever 4 with the associated end of arm 3, wherein the throttle valve is slightly opened from the idling position shown by phantom lines to a degree sufficient to effect complete combustion and to suppress emission of uncombusted components. After the throttle valve has been set to the abovementioned position, the vacuum in the intake tube increases and, since the opening end 13 is now positioned downstream of the throttle valve 2, the vacuum in the intake tube is transmitted through the conduit means 11 toward the diaphragm means. However, due to the use of the constricting means 11 and an air chamber 12 operating as an accumulator, the effective transmission of the vacuum from the open end 13 to the diaphragm chamber 9 is delayed. When the diaphragm chamber 9 has been effectively evacuated, the diaphragm 7 is pulled down against the action of the spring 6, moving the rod 8 downward and turning the lever 4 clockwise to disengage it from the arm 3. Thus, the throttle valve 2 returns to its idling position as shown by phantom lines. Therefore, the throttle valve 2 is kept at the HC reduction opening position for a period determined by the constricting means 17 and the air chamber 12.
After the throttle valve has been returned to the idling position, if the acceleration pedal is depressed to start the vehicle, the throttle valve 2 is opened by traversing the open end 13 so that the opening is positioned upstream thereof, whereby atmospheric pressure is again introduced into the diaphragm chamber 9. In this case, a time delay of the same kind is effected by the constricting means 17 and the air chamber 12 before the diaphragm chamber 9 is completely filled with air at atmospheric pressure. Therefore, in a vehicle equipped with the conventional throttle positioner as explained above, if the acceleration pedal has once been depressed to start the vehicle thereby opening the throttle valve from the idling position, and immediately thereafter, the acceleration pedal is released to effect deceleration, the lever 4 has not yet been returned to the position to hold the throttle valve 2 at said HC reduction opening position due to the aforementioned delay in transmitting atmospheric pressure into the diaphragm chamber 9 and, accordingly, the throttle valve is returned to the idling position beyond the HC reduction opening position, whereby a high emission of HC in the exhaust gas occurs. Furthermore, the operating time to set the stopper screw 14 of the lever 4 to the throttle positioner operating position or to release it from its operating position is determined by the constricting means 17 and the air chamber 12 provided in the conduit means 11 and, if the period during which the stopper screw 14 is set at the throttle positioner operating position is to be longer, the time required for setting the stopper screw 14 becomes also longer. In other words, it has been impossible to determine independently the period in which the throttle positioner operating condition is held and the time required for the setting.